This invention relates to a seal system for a turbomachine, and in particular, to a seal system operable to prevent migration of oil into the portion of the turbomachine having process gas flowing therethrough.
It is well recognized that seal oil or lubricating oil must, in most cases, be prevented from migrating into the portion of a turbomachine in which process gas is flowing to prevent contamination of the process gas. Mechanical seals are generally employed in an attempt to prevent the flow of oil into the process gas stream. Similarly, fluid seals, such as a buffer fluid, may also be employed either independently, or in conjunction with mechanical seals, in an attempt to prevent undesired oil flow.
Although in general, the use of such mechanical and/or fluid seals are effective in limiting the migration of oil into the process gas zone of a turbomachine, in some cases some migration of oil has occurred. For example, during periods of startup or shutdown, the pressure in the portion of the turbomachine containing the process gas will decrease, creating operating conditions during which undesirable oil migration will more likely occur, particularly in machines utilizing only mechanical seals. The inclusion of buffer fluid seal systems have not always increased the reliability of the seal system as desired. Further, buffer seal systems are relatively expensive to manufacture and use, and are rather difficult to maintain. It is therefore desirable to provide a seal system which operates effectively and efficiently and which may be provided at minimal additional cost.